1. Technical Field
The present disclosure relates to an optical component, and in particular relates to a mask structure.
2. Description of the Related Art
Lithography has been used in the semiconductor industry as one of critical techniques in manufacturing integrated circuits (ICs). Typically, lithography is used to create a pattern on a resist layer on a substrate such as a semiconductor wafer, with the pattern being an IC layout later to be formed on the substrate through the performance of subsequent steps such as etching and other steps. The wavelength of light used in lithography determines the pattern size and thus the feature size of the IC layout. Generally, feature size is proportional to the wavelength of the light used in the lithography process. As demand for semiconductor devices with smaller IC features and higher integration densities continues to grow, the wavelength of light has to decrease. Currently, lithography with wavelengths into the deep ultraviolet region (using deep ultraviolet light at 193 nm) has been used to create smaller IC features. However, for even smaller IC features to be created, even shorter wavelengths have to be used. Thus, to overcome the limiting resolution of patterns formed in the lithography process next generation lithography has been developed, and extreme ultraviolet lithography (EUVL) (using 13.5 nm EUV light) has emerged as one promising candidate.
Due to great absorption of EUV light in many materials, one major difference between EUVL and conventional lithography techniques using visible or UV light is that EUV relies on the principle of light reflection since it is almost impossible to use refractive optical elements such as lenses and transmission masks. In EUVL, a mask including an optical reflection structure and an absorber pattern corresponding to a pattern to be formed on a wafer is used, and when an EUV light is projected onto the mask, the absorber pattern absorbs a portion of the light and the optical reflection structure reflects the remainder of light onto the wafer to form the pattern. However, the performance of currently available EUV masks has not been satisfactory in all aspects. Thus, an improved EUV mask is needed.